35 research outputs found
Disentangling 2:1 resonant radial velocity orbits from eccentric ones and a case study for HD 27894
In radial velocity observations, a pair of extrasolar planets near a 2:1
orbital resonance can be misinterpreted as a single eccentric planet, if data
are sparse and measurement precision insufficient to distinguish between these
models. We determine the fraction of alleged single-planet RV detected systems
for which a 2:1 resonant pair of planets is also a viable model and address the
question of how the models can be disentangled. By simulation we quantified the
mismatch arising from applying the wrong model. Model alternatives are
illustrated using the supposed single-planet system HD 27894 for which we also
study the dynamical stability of near-2:1 resonant solutions. From the data
scatter around the fitted single-planet Keplerians, we find that for of
the putative single-planet systems, a 2:1 resonant pair cannot be
excluded as a viable model, since the error due to the wrong model is smaller
than the scatter. For stars -probabilities can be used to reject
the Keplerian models with a confidence of for of the stars and
with for of the stars. For HD 27894 a considerable fit
improvement is obtained when adding a low-mass planet near half the orbital
period of the known Jovian planet. Dynamical analysis demonstrates that this
system is stable when both planets are initially placed on circular orbits. For
fully Keplerian orbits a stable system is only obtained if the eccentricity of
the inner planet is constrained to . A large part of the allegedly RV
detected single-planet systems should be scrutinized in order to determine the
fraction of systems containing near-2:1 resonant pairs of planets. Knowing the
abundance of such systems will allow us to revise the eccentricity distribution
for extrasolar planets and provide direct constraints for planetary system
formation.Comment: 12 pages, 8 figures, one of them composed by two files, accepted by
A&A, citations may appear in a non-standard way (double brackets) due to
reformatting needs. Abstract slightly adjuste
New HARPS and FEROS observations of GJ1046
In this paper we present new precise Doppler data of GJ1046 taken between
November 2005 and July 2018 with the HARPS and the FEROS high-resolution
spectographs. In addition, we provide a new stellar mass estimate of GJ1046 and
we update the orbital parameters of the GJ1046 system. These new data and
analysis could be used together with the GAIA epoch astrometry, when available,
for braking the degeneracy and revealing the true mass of the GJ1046
system.Comment: 2 pages, 1 figure, 1 table with RV data (available only in the
Astro-PH version of the paper), Accepted by RNAA
Rossiter-McLaughlin Observations of 55 Cnc e
We present Rossiter-McLaughlin observations of the transiting super-Earth 55
Cnc e collected during six transit events between January 2012 and November
2013 with HARPS and HARPS-N. We detect no radial-velocity signal above 35 cm/s
(3-sigma) and confine the stellar v sin i to 0.2 +/- 0.5 km/s. The star appears
to be a very slow rotator, producing a very low amplitude Rossiter-McLaughlin
effect. Given such a low amplitude, the Rossiter-McLaughlin effect of 55 Cnc e
is undetected in our data, and any spin-orbit angle of the system remains
possible. We also performed Doppler tomography and reach a similar conclusion.
Our results offer a glimpse of the capacity of future instrumentation to study
low amplitude Rossiter-McLaughlin effects produced by super-Earths.Comment: Accepted for publication in ApJ Letter
A Spectral Survey of WASP-19b with ESPRESSO
High resolution precision spectroscopy provides a multitude of robust
techniques for probing exoplanetary atmospheres. We present multiple
VLT/ESPRESSO transit observations of the hot-Jupiter exoplanet WASP-19b with
previously published but disputed atmospheric features from low resolution
studies. Through spectral synthesis and modeling of the Rossiter-McLaughlin
(RM) effect we calculate stellar, orbital and physical parameters for the
system. From narrow-band spectroscopy we do not detect any of H\,I, Fe\,I,
Mg\,I, Ca\,I, Na\,I and K\,I neutral species, placing upper limits on their
line contrasts. Through cross correlation analyses with atmospheric models, we
do not detect Fe\,I and place a 3 upper limit of
on its mass
fraction, from injection and retrieval. We show the inability to detect the
presence of HO for known abundances, owing to lack of strong absorption
bands, as well as relatively low S/N ratio. We detect a barely significant peak
(3.02\,\,0.15\,) in the cross correlation map for TiO, consistent
with the sub-solar abundance previously reported. This is merely a hint for the
presence of TiO and does \textit{not} constitute a confirmation. However, we do
confirm the presence of previously observed enhanced scattering towards blue
wavelengths, through chromatic RM measurements, pointing to a hazy atmosphere.
We finally present a reanalysis of low resolution transmission spectra of this
exoplanet, concluding that unocculted starspots alone cannot explain previously
detected features. Our reanalysis of the FORS2 spectra of WASP-19b finds a
\,100 sub-solar TiO abundance, precisely constrained to
, consistent with the TiO hint
from ESPRESSO. We present plausible paths to reconciliation with other
seemingly contradicting results.Comment: 24 pages, 16 figures, submitted to MNRA
ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of , but no evidence of Na or K
We present a new ground-based visual transmission spectrum of the hot Jupiter
WASP-43b, obtained as part of the ACCESS Survey. The spectrum was derived from
four transits observed between 2015 and 2018, with combined wavelength coverage
between 5,300 \r{A}-9,000 \r{A} and an average photometric precision of 708 ppm
in 230 \r{A} bins. We perform an atmospheric retrieval of our transmission
spectrum combined with literature HST/WFC3 observations to search for the
presence of clouds/hazes as well as Na, K, H, and planetary
absorption and stellar spot contamination over a combined spectral range of
5,318 \r{A}-16,420 \r{A}. We do not detect a statistically significant presence
of Na I or K I alkali lines, or H in the atmosphere of WASP-43b. We
find that the observed transmission spectrum can be best explained by a
combination of heterogeneities on the photosphere of the host star and a clear
planetary atmosphere with . This model yields a log-evidence of
higher than a flat (featureless) spectrum. In particular, the
observations marginally favor the presence of large, low-contrast spots over
the four ACCESS transit epochs with an average covering fraction and temperature contrast . Within the planet's atmosphere, we recover a log
volume mixing ratio of , which is consistent with
previous abundance determinations for this planet.Comment: 27 pages, 18 figures, 7 tables. Accepted for publication in AJ.
Updated affiliation
ACCESS: A featureless optical transmission spectrum for WASP-19b from Magellan/IMACS
The short period (-day) transiting exoplanet WASP-19b is an exceptional
target for transmission spectroscopy studies, due to its relatively large
atmospheric scale-height ( km) and equilibrium temperature ( K). Here we report on six precise spectroscopic Magellan/IMACS
observations, five of which target the full optical window from m
and one targeting the m blue-optical range. Five of these datasets
are consistent with a transmission spectrum without any significant spectral
features, while one shows a significant slope as a function of wavelength,
which we interpret as arising from photospheric heterogeneities in the star.
Coupled with HST/WFC3 infrared observations, our optical/near-infrared
measurements point to the presence of high altitude clouds in WASP-19b's
atmosphere in agreement with previous studies. Using a semi-analytical
retrieval approach, considering both planetary and stellar spectral features,
we find a water abundance consistent with solar for WASP-19b and strong
evidence for sub-solar abundances for optical absorbers such as TiO and Na; no
strong optical slope is detected, which suggests that if hazes are present,
they are much weaker than previously suggested. In addition, two spot-crossing
events are observed in our datasets and analyzed, including one of the first
unambiguously detected bright spot-crossing events on an exoplanet host star.Comment: 20 pages (plus 5 for the Appendix), 17 figures, 5 tables. MNRAS, in
pres
ACCESS & LRG-BEASTS: a precise new optical transmission spectrum of the ultrahot Jupiter WASP-103b
We present a new ground-based optical transmission spectrum of the ultrahot
Jupiter WASP-103b (K). Our transmission spectrum is the result
of combining five new transits from the ACCESS survey and two new transits from
the LRG-BEASTS survey with a reanalysis of three archival Gemini/GMOS transits
and one VLT/FORS2 transit. Our combined 11-transit transmission spectrum covers
a wavelength range of 3900--9450A with a median uncertainty in the transit
depth of 148 parts-per-million, which is less than one atmospheric scale height
of the planet. In our retrieval analysis of WASP-103b's combined optical and
infrared transmission spectrum, we find strong evidence for unocculted bright
regions () and weak evidence for HO (), HCN
(), and TiO (), which could be responsible for
WASP-103b's observed temperature inversion. Our optical transmission spectrum
shows significant structure that is in excellent agreement with the extensively
studied ultrahot Jupiter WASP-121b, for which the presence of VO has been
inferred. For WASP-103b, we find that VO can only provide a reasonable fit to
the data if its abundance is implausibly high and we do not account for stellar
activity. Our results highlight the precision that can be achieved by
ground-based observations and the impacts that stellar activity from F-type
stars can have on the interpretation of exoplanet transmission spectra.Comment: 33 pages, 17 figures, 7 tables. Accepted for publication in A
ACCESS: Confirmation of no potassium in the atmosphere of WASP-31b
We present a new optical (400-950nm) transmission spectrum of the hot Jupiter
WASP-31b (M=0.48 MJ; R= 1.54 RJ; P=3.41 days), obtained by combining four
transits observations. These transits were observed with IMACS on the Magellan
Baade Telescope at Las Campanas Observatory as part of the ACCESS project. We
investigate the presence of clouds/hazes in the upper atmosphere of this planet
as well as the contribution of stellar activity on the observed features. In
addition, we search for absorption features of the alkali elements Na I and K
I, with particular focus on K I, for which there have been two previously
published disagreeing results. Observations with HST/STIS detected K I, whereas
ground-based low- and high-resolution observations did not. We use equilibrium
and non-equilibrium chemistry retrievals to explore the planetary and stellar
parameter space of the system with our optical data combined with existing
near-IR observations. Our best-fit model is that with a scattering slope
consistent with a Rayleigh slope (alpha=5.3+2.9-3.1), high-altitude clouds at a
log cloud top pressure of -3.6+2.7-2.1 bars, and possible muted H2O features.
We find that our observations support other ground-based claims of no K I.
Clouds are likely why signals like H2O are extremely muted and Na or K cannot
be detected. We then juxtapose our Magellan/IMACS transmission spectrum with
existing VLT/FORS2, HST/WFC3, HST/STIS, and Spitzer observations to further
constrain the optical-to-infrared atmospheric features of the planet. We find
that a steeper scattering slope (alpha = 8.3+/-1.5) is anchored by STIS
wavelengths blueward of 400 nm and only the original STIS observations show
significant potassium signal.Comment: Accepted 14 September 2020 by A